1) Field of the Invention
The present invention relates to hub drives for vehicles, in particular a steerable land vehicle.
2) Description of Related Art
Hub drives are known in hybrid vehicles comprising four or more driven wheels each provided with an independent electric motor driving a gearbox mounted in the hub of the wheel. Power for the motors is usually provided by a battery, which is itself normally charged by a combustion engine mounted in the vehicle. Such an arrangement is efficient for vehicles operating in various conditions such as public transport. They are also effective for certain military vehicles for providing stealth operation occasionally when the combustion engine is temporarily stopped.
The requirements for hub drives are multifarious. They should be light since they are mounted on unsuspended parts of the vehicle, yet they need to meet respectable power expectations. Indeed, such expectations are not just in respect of peak torques that the motor and associated gearbox deliver (perhaps in the region of 20,000 Nm, with continuous torque at about half this), but also in respect of the instantaneous torques they may experience in the field. Such torques may be generated, for example, through forced acceleration due to the vehicle dropping onto a wheel from a height. Such torques that the drive might be expected to handle in some vehicles are in the region of 70,000 Nm.
Hub drives also need to be accessible, so that they can be serviced easily when faults develop. They require effective braking systems. Braking torque requirements are invariably much higher than required drive torques.
Frequently, it is desirable to employ the motor, at least partially in this respect, to assist braking and feedback power to the battery charging circuit. An efficient control system is also required to synchronise drive to each wheel to ensure efficient operation, and this may include anti-slip and anti-lock functions, yaw control and vehicle steering.
Hub drives should be reliable, particularly in military vehicles. Active control of tyre pressures is also desirable in such vehicles, and facilities for this impact the design of hub drives.
WO-A-9723363 discloses a drive having a motor in a casing forming a frame suspended in the vehicle. The motor drives a shaft forming a sun wheel for a planetary gearbox, whose planet gears drive a hub rotationally mounted on an extension of the frame around the shaft. A clutch selectively locks a planet wheel to the frame to transmit drive.
U.S. Pat. No. 5,163,528 and U.S. Pat. No. 5,014,800 both disclose a wheel motor having a stator fixed to a casing and a rotatable rotor and an integrated reduction gear.
U.S. Pat. No. 4,389,586 discloses a wheel drive having an inboard mounting frame tube incorporating planetary gears and an motor removal from an outboard side, the wheel being mounted on large diameter bearings on the frame tube.
U.S. Pat. No. 5,472,059 discloses a frame on the inboard side of which is mounted a motor whose drive shaft extends through the frame and on a neck of which frame is mounted a wheel hub. A planetary gearbox is on the outboard end of the frame and shaft and drives the hub.
U.S. Pat. No. 5,382,854 discloses a wheel drive in which a stator is fixed in a frame element, and a rotor drives the sun wheel of a planetary reduction gear disposed within the confines of the rotor and arranged to drive a hub rotationally mounted in the frame. The frame forms a sealed casing receiving oil which is circulated to both cool the motor and lubricate the planetary gear system.
In none of the aforementioned arrangements is substantial dismantling of the drive possible without removing the wheels of the vehicle.